Requirements for robust IP/UDP/RTP header compression
RFC 3096

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Network Working Group                               M. Degermark, Editor
Request for Comments: 3096                         University of Arizona
Category: Informational                                        July 2001

         Requirements for robust IP/UDP/RTP header compression

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This document contains requirements for robust IP/UDP/RTP (Internet
   Protocol/User Datagram Protocol/Real-Time Transport Protocol) header
   compression to be developed by the ROHC (Robust Header Compression)
   WG.  It is based on the ROHC charter, discussions in the WG, the 3GPP
   document "3GPP TR 23.922", version 1.0.0 of October 1999, as well as
   contributions from 3G.IP.

1.  Introduction

   The goal of the ROHC WG is to develop header compression schemes that
   perform well over links with high error rates and long link round
   trip times.  The schemes must perform well for cellular links built
   using technologies such as WCDMA, EDGE, and CDMA-2000.  However, the
   schemes should also be applicable to other future link technologies
   with high loss and long round trip times.

   The following requirements have, more or less arbitrarily, been
   divided into three groups.  The first group deals with requirements
   concerning the impact of an header compression scheme on the rest of
   the Internet infrastructure.  The second group concerns what kind of
   headers that must be compressed efficiently.  The final group
   concerns efficiency requirements and requirements which stem from the
   properties of the anticipated link technologies.

2. Header compression requirements

   Several current standardization efforts in the cellular arena aim at
   supporting voice over IP and other real-time services over IP, e.g.,
   GERAN (specified by the ETSI SMG2 standards group), and UTRAN

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RFC 3096            Requirements for IP/UDP/RTP ROHC           July 2001

   (specified by the 3GPP standards organization).  It is critical for
   these standardization efforts that a suitable header compression
   scheme is developed before completion of the Release 2000 standards.
   Therefore, it is imperative that the ROHC WG keeps its schedule.

2.1 Impact on Internet infrastructure

   1. Transparency: When a header is compressed and then decompressed,
   the resulting header must be semantically identical to the original
   header.  If this cannot be achieved, the packet containing the
   erroneous header must be discarded.

   Justification: The header compression process must not produce
   headers that might cause problems for any current or future part of
   the Internet infrastructure.

   2. Ubiquity: Must not require modifications to existing IP (v4 or
   v6), UDP, or RTP implementations.

   Justification: Ease of deployment.

   Note: The ROHC WG may recommend changes that would increase the
   compression efficiency for the RTP streams emitted by
   implementations.  However, ROHC cannot rely on such recommendations
   being followed.

2.2 Supported headers and kinds of RTP streams

   1. IPv4 and IPv6: Must support both IPv4 and IPv6.

   Justification: IPv4 and IPv6 will both be around during the
   foreseeable future.

   2. Mobile IP: The kinds of headers used by Mobile IP{v4,v6} should be
   compressed efficiently.  For IPv4 these include headers of tunneled
   packets.  For IPv6 these include headers containing the Routing
   Header, the Binding Update Destination Option, and the Home Address
   option.

   Justification: It is very likely that Mobile IP will be used by
   cellular devices.

   3. Genericity: Must support compression of headers of arbitrary RTP
   streams.

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RFC 3096            Requirements for IP/UDP/RTP ROHC           July 2001

   Justification: There must be a generic scheme which can compress
   reasonably well for any payload type and traffic pattern.  This does
   not preclude optimizations for certain media types where the traffic
   pattern is known, e.g., for low-bandwidth voice and low-bandwidth
   video.

   Note: This applies to the RTP stream before as well as after it has
   passed through an internet.

   4. IPSEC: ROHC should be able to compress headers containing IPSEC
   subheaders.

   Note: It is of course not possible to compress the encrypted part of
   an ESP header, nor the cryptographic data in an AH header.

2.3 Efficiency

   1. Performance/Spectral Efficiency: Must provide low relative
   overhead under expected operating conditions; compression efficiency
   should be better than for RFC 2508 under equivalent operating
   conditions.  The error rate should only marginally increase the